Self-Renewal Understood

A paper to be published online by Nature (Vol. 441, No. 7095)identifies a molecule that endows embryonic stem (ES) cells with their revered properties: the ability to self-renew and 'pluripotency', the ability to make numerous other cell types. Molecules such as this might one day be used to convert a patient's regular, somatic cell into an ES cell, perhaps avoiding the ethically contentious extraction of ES cells from human embryos.

Stem-cell biologists know that fusing an ES cell with a somatic cell can bestow the latter with pluripotency. Austin Smith and his colleagues show that a protein called Nanog, which is manufactured in young embryos, is responsible: they showed that mouse ES cells making extra Nanog protein can convert neural stem cells into pluripotent cells at a much higher efficiency. They propose that Nanog directs the ES cell machinery to erase old patterns of gene activity and install new pluripotent ones.